This invention relates generally to a device for ocean offshore and other dredging operations. The inventor calls this device the "STUMP" dredge, a descriptive acronym standing for "submersible transportable utility marine pump." Besides serving as a dredge, the STUMP can accomplish other operations, such as augering, trenching and serving as a pump sub-station or as a base for divers.
The prior art contains devices which have some of the features of the STUMP, but no prior device possesses all of the desirable features and capabilities of the STUMP. Because of the efficiency of the STUMP, due in part to its stability and its containment of its dredge pump within a few feet of the material being dredged rather than at the surface, and because it combines many desirable features within a relatively small transportable device, many underwater operations previously too costly are now economically feasible.
According to the National Shoreline Study begun in 1970 by the U.S. Army Corps of Engineers, about 8% of 37,000 miles of U.S. coastline have eroding beaches which are in "critical" condition. "Critical" condition means that the cost of nourishing the beach is less than the value of the beach and the property it protects. To calculate the cost of beach nourishment against the value of property, a unit cost per cubic yard of sand or other material placed on the beach must be calculated.
Dredging projects have different degrees of difficulty and employ different equipment. Dredging in protected waters can be done at approximately one-fourth the cost of open sea dredging. The large cost differential is due to the down-time of equipment resulting from such causes as inability to operate during bad weather, or standing by for repairs to damage to equipment while operating in rough seas. The STUMP substantially lowers the cost of open sea dredging because the STUMP can operate continuously and nearly as well in rough sea conditions as other dredges operate in protected waters. Such rough water operations are possible because the STUMP is a highly mobile, submersible self-contained dredging device which requires no surface operation or direction when manned, and because the STUMP can take on ballast to lower its center of gravity and submerge it to a selected depth while exposing only a small snorkle to rough water surface conditions.
In 1906, U.S. Pat. No. 813,935 was granted to Avery for a submarine dredge. This dredge was limited in several respects. Its power was supplied through lines from a tender vessel or from shore. It was wheeled, whereas wheels and tracks have generally not proven successful for use in submersible dredges; and it had ballast tanks which were not large enough in comparison to the total volume of the vessel to give the device the stability necessary to operate in heavy offshore wave conditions.
In 1908, U.S. Pat. No. 885,930 was granted to Lake for a dredging device which was much more mobile and controllable than Avery's dredge because it was attached to a tender vessel and to anchor weights by cables, the cables being controlled by winches on the dredge to move it as required. Lake's device was an improvement over Avery in that it had cutting blades that could aid in dredging hard ocean bottoms. However, because Lake's device required attachment to and dependence on a tender vessel at the water surface, as well as direct contact with the ocean bed, structural failures became probable if wave heights increased over about four feet.
In 1908, U.S. Pat. No. 939,227 was granted to Diehle for a variation of the Lake type device. Diehle's device suffered from the same disadvantages mentioned with reference to the Lake device, such as long down-time during rough seas and an over-all inefficient pumping system.
In 1919, U.S. Pat. No. 1,321,562 was granted to Sisson for a submarine vessel designed primarily as a salvaging device. This vessel contained its own power source and had external propellers and rudders for manuevering. However, the device could not take on ballast to change its density and its submerged position, and, since it is lighter than sea water, it required constant operation of a propeller to supply a downward thrust to submerge it and keep it submerged. The device had to be attached to a tender ship by a cable and contained a limited compressed air supply.
In 1934, U.S. Pat. No. 1,948,934 was granted to O'Rourke for a submarine air lock, which, like Sisson's device, was used primarily as a salvage vessel. O'Rourke's device could change its density by lowering weights to the ocean floor, said weights being attached to the device by cables. But the device had no propellers or rudders for manuevering it. O'Rourke's device was constantly dependent upon a surface vessel for a supply of fresh air.
In 1950, U.S. Pat. No. 2,519,458 granted to Goodman disclosed a traveling underwater compressed air working chamber which combined propeller manueverability with the ability to change density, which features made it possible for the device to operate freely from a surface tender vessel. The device was used as a base for divers working in a surrounding underwater area. Since the device had no snorkel and was free of surface attachments, it had a limited compressed air supply. This feature and others limited the usefulness of the device to a temporary base station for divers.
In 1952, U.S. Pat. No. 2,585,712 was granted to Wiggins for a diving apparatus similar to that of Goodman which was quite stable due to the provision of feet which could take on ballast. The device could stay down indefinitely since it received air from the surface, but required a surface vessel to attend it constantly.
In 1968, U.S. Pat. No. 3,369,368 granted to Wilson disclosed a diving structure which combined the features of the Goodman and Wiggins devices. The Wilson device had propellers for manueverability, ballast tanks, and feet to take on ballast for stability. If a tender vessel was present the Wilson device could get air from it, or it could use compressed air in tanks within the device. Wilson's device also provided means for spraying jets of water from feet supporting the device. The jets were used only to free the feet from the bottom after they had settled into the ocean floor. The Wilson device had limited versatility since it could serve only as a base for divers.
As can be seen from this cursory review of the prior art, many different types of underwater devices have been designed, each primarily for some specific type of underwater operation. Each prior device was implicitly limited to the performance of only the operation for which it was designed. Similarly, in each prior device the provision of certain advantageous features therein meant accompanying disadvantages, such as a limited compressed air supply in devices independent of a tender vessel, and ability to achieve a high degree of manueverability only at the expense of limited stability.